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 $239.53   8.763%   $260.52   $260.52   $260.50   $260.50  
  Purchase #2 $118.57   3.708%   $122.9666   $122.97   $122.95   $123.00  
  Purchase #3 $77.93   8.521%   $84.5704   $84.57   $84.55   $84.60  
  Purchase #4 $238.84   7.112%   $255.8263   $255.83   $255.85   $255.80  
  Purchase #5 $26.93   5.640%   $28.4489   $28.45   $28.45   $28.40  
  Purchase #6 $47.81   3.701%   $49.5794   $49.58   $49.60   $49.60  
  Purchase #7 $192.63   9.300%   $210.5446   $210.54   $210.55   $210.50  
  7 purchase totals = $942.24       $1,012.4562   $1,012.46   $1,012.45   $1,012.40