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 $126.61   11.658%   $141.3702   $141.37   $141.35   $141.40  
  Purchase #2 $223.30   9.266%   $243.991   $243.99   $244.00   $244.00  
  Purchase #3 $104.89   4.795%   $109.9195   $109.92   $109.90   $109.90  
  Purchase #4 $60.99   7.183%   $65.3709   $65.37   $65.35   $65.40  
  Purchase #5 $90.71   4.546%   $94.8337   $94.83   $94.85   $94.80  
  Purchase #6 $75.42   6.234%   $80.1217   $80.12   $80.10   $80.10  
  Purchase #7 $206.43   7.511%   $221.935   $221.94   $221.95   $221.90  
  7 purchase totals = $888.35       $957.5420   $957.54   $957.50   $957.50