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 $149.59   9.526%   $163.8399   $163.84   $163.85   $163.80  
  Purchase #2 $177.66   12.353%   $199.6063   $199.61   $199.60   $199.60  
  Purchase #3 $97.78   4.628%   $102.3053   $102.31   $102.30   $102.30  
  Purchase #4 $225.53   11.675%   $251.8606   $251.86   $251.85   $251.90  
  Purchase #5 $218.63   4.314%   $228.0617   $228.06   $228.05   $228.10  
  Purchase #6 $45.57   10.490%   $50.3503   $50.35   $50.35   $50.40  
  Purchase #7 $243.49   4.525%   $254.5079   $254.51   $254.50   $254.50  
  7 purchase totals = $1,158.25       $1,250.5320   $1,250.54   $1,250.50   $1,250.60