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 $7.87   3.467%   $8.1429   $8.14   $8.15   $8.10  
  Purchase #2 $25.28   12.809%   $28.5181   $28.52   $28.50   $28.50  
  Purchase #3 $117.39   4.230%   $122.3556   $122.36   $122.35   $122.40  
  Purchase #4 $52.42   9.419%   $57.3574   $57.36   $57.35   $57.40  
  Purchase #5 $203.29   9.399%   $222.3972   $222.40   $222.40   $222.40  
  Purchase #6 $54.40   8.757%   $59.1638   $59.16   $59.15   $59.20  
  Purchase #7 $47.99   3.594%   $49.7148   $49.71   $49.70   $49.70  
  7 purchase totals = $508.64       $547.6498   $547.65   $547.60   $547.70