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 $147.30   8.111%   $159.2475   $159.25   $159.25   $159.20  
  Purchase #2 $177.55   11.831%   $198.5559   $198.56   $198.55   $198.60  
  Purchase #3 $138.52   10.808%   $153.4912   $153.49   $153.50   $153.50  
  Purchase #4 $200.80   10.246%   $221.374   $221.37   $221.35   $221.40  
  Purchase #5 $236.52   10.330%   $260.9525   $260.95   $260.95   $261.00  
  Purchase #6 $211.87   13.819%   $241.1483   $241.15   $241.15   $241.10  
  Purchase #7 $58.31   11.344%   $64.9247   $64.92   $64.90   $64.90  
  7 purchase totals = $1,170.87       $1,299.6941   $1,299.69   $1,299.65   $1,299.70