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 $53.46   6.111%   $56.7269   $56.73   $56.75   $56.70  
  Purchase #2 $76.94   6.870%   $82.2258   $82.23   $82.25   $82.20  
  Purchase #3 $167.59   3.677%   $173.7523   $173.75   $173.75   $173.80  
  Purchase #4 $250.95   7.567%   $269.9394   $269.94   $269.95   $269.90  
  Purchase #5 $109.35   13.676%   $124.3047   $124.30   $124.30   $124.30  
  Purchase #6 $181.68   12.149%   $203.7523   $203.75   $203.75   $203.80  
  Purchase #7 $184.83   4.640%   $193.4061   $193.41   $193.40   $193.40  
  7 purchase totals = $1,024.80       $1,104.1075   $1,104.11   $1,104.15   $1,104.10