Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.58   8.748%   $226.8266   $226.83   $226.85   $226.80  
  Purchase #2 $100.82   8.818%   $109.7103   $109.71   $109.70   $109.70  
  Purchase #3 $185.93   8.474%   $201.6857   $201.69   $201.70   $201.70  
  Purchase #4 $102.64   13.558%   $116.5559   $116.56   $116.55   $116.60  
  Purchase #5 $248.35   11.777%   $277.5982   $277.60   $277.60   $277.60  
  Purchase #6 $181.34   12.483%   $203.9767   $203.98   $204.00   $204.00  
  Purchase #7 $138.93   6.715%   $148.2591   $148.26   $148.25   $148.30  
  7 purchase totals = $1,166.59       $1,284.6125   $1,284.63   $1,284.65   $1,284.70