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 $213.63   6.353%   $227.2019   $227.20   $227.20   $227.20  
  Purchase #2 $47.65   13.187%   $53.9336   $53.93   $53.95   $53.90  
  Purchase #3 $146.44   6.843%   $156.4609   $156.46   $156.45   $156.50  
  Purchase #4 $79.32   6.685%   $84.6225   $84.62   $84.60   $84.60  
  Purchase #5 $50.80   9.496%   $55.624   $55.62   $55.60   $55.60  
  Purchase #6 $212.75   11.809%   $237.8736   $237.87   $237.85   $237.90  
  Purchase #7 $47.26   8.241%   $51.1547   $51.15   $51.15   $51.20  
  7 purchase totals = $797.85       $866.8712   $866.85   $866.80   $866.90