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 $58.87   3.214%   $60.7621   $60.76   $60.75   $60.80  
  Purchase #2 $99.52   7.576%   $107.0596   $107.06   $107.05   $107.10  
  Purchase #3 $27.55   3.382%   $28.4817   $28.48   $28.50   $28.50  
  Purchase #4 $60.41   12.483%   $67.951   $67.95   $67.95   $68.00  
  Purchase #5 $38.49   7.155%   $41.244   $41.24   $41.25   $41.20  
  Purchase #6 $184.30   8.309%   $199.6135   $199.61   $199.60   $199.60  
  Purchase #7 $226.84   8.241%   $245.5339   $245.53   $245.55   $245.50  
  7 purchase totals = $695.98       $750.6458   $750.63   $750.65   $750.70