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 $193.35   5.517%   $204.0171   $204.02   $204.00   $204.00  
  Purchase #2 $141.74   6.104%   $150.3918   $150.39   $150.40   $150.40  
  Purchase #3 $216.42   10.387%   $238.8995   $238.90   $238.90   $238.90  
  Purchase #4 $126.80   4.548%   $132.5669   $132.57   $132.55   $132.60  
  Purchase #5 $179.51   11.778%   $200.6527   $200.65   $200.65   $200.70  
  Purchase #6 $181.79   6.544%   $193.6863   $193.69   $193.70   $193.70  
  Purchase #7 $115.61   13.683%   $131.4289   $131.43   $131.45   $131.40  
  7 purchase totals = $1,155.22       $1,251.6432   $1,251.65   $1,251.65   $1,251.70