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 $116.80   5.752%   $123.5183   $123.52   $123.50   $123.50  
  Purchase #2 $105.96   10.182%   $116.7488   $116.75   $116.75   $116.70  
  Purchase #3 $199.59   7.662%   $214.8826   $214.88   $214.90   $214.90  
  Purchase #4 $25.89   9.148%   $28.2584   $28.26   $28.25   $28.30  
  Purchase #5 $126.50   9.851%   $138.9615   $138.96   $138.95   $139.00  
  Purchase #6 $235.76   5.467%   $248.649   $248.65   $248.65   $248.60  
  Purchase #7 $60.79   6.194%   $64.5553   $64.56   $64.55   $64.60  
  7 purchase totals = $871.29       $935.5739   $935.58   $935.55   $935.60