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 $152.27   8.123%   $164.6389   $164.64   $164.65   $164.60  
  Purchase #2 $214.81   6.436%   $228.6352   $228.64   $228.65   $228.60  
  Purchase #3 $151.95   8.833%   $165.3717   $165.37   $165.35   $165.40  
  Purchase #4 $241.73   6.796%   $258.158   $258.16   $258.15   $258.20  
  Purchase #5 $231.78   6.412%   $246.6417   $246.64   $246.65   $246.60  
  Purchase #6 $219.52   4.642%   $229.7101   $229.71   $229.70   $229.70  
  Purchase #7 $178.40   7.785%   $192.2884   $192.29   $192.30   $192.30  
  7 purchase totals = $1,390.46       $1,485.4440   $1,485.45   $1,485.45   $1,485.40