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 $48.47   10.752%   $53.6815   $53.68   $53.70   $53.70  
  Purchase #2 $132.33   11.743%   $147.8695   $147.87   $147.85   $147.90  
  Purchase #3 $62.78   4.600%   $65.6679   $65.67   $65.65   $65.70  
  Purchase #4 $216.42   11.223%   $240.7088   $240.71   $240.70   $240.70  
  Purchase #5 $63.93   6.457%   $68.058   $68.06   $68.05   $68.10  
  Purchase #6 $80.80   4.600%   $84.5168   $84.52   $84.50   $84.50  
  Purchase #7 $121.95   3.234%   $125.8939   $125.89   $125.90   $125.90  
  7 purchase totals = $726.68       $786.3964   $786.40   $786.35   $786.50