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 $173.25   12.299%   $194.558   $194.56   $194.55   $194.60  
  Purchase #2 $44.74   9.437%   $48.9621   $48.96   $48.95   $49.00  
  Purchase #3 $76.65   3.761%   $79.5328   $79.53   $79.55   $79.50  
  Purchase #4 $25.37   10.459%   $28.0234   $28.02   $28.00   $28.00  
  Purchase #5 $236.86   7.609%   $254.8827   $254.88   $254.90   $254.90  
  Purchase #6 $162.73   12.830%   $183.6083   $183.61   $183.60   $183.60  
  Purchase #7 $206.96   12.460%   $232.7472   $232.75   $232.75   $232.70  
  7 purchase totals = $926.56       $1,022.3145   $1,022.31   $1,022.30   $1,022.30