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 $238.73   5.871%   $252.7458   $252.75   $252.75   $252.70  
  Purchase #2 $83.43   6.241%   $88.6369   $88.64   $88.65   $88.60  
  Purchase #3 $97.26   4.436%   $101.5745   $101.57   $101.55   $101.60  
  Purchase #4 $176.93   3.723%   $183.5171   $183.52   $183.50   $183.50  
  Purchase #5 $55.99   4.218%   $58.3517   $58.35   $58.35   $58.40  
  Purchase #6 $127.75   3.835%   $132.6492   $132.65   $132.65   $132.60  
  Purchase #7 $59.34   7.596%   $63.8475   $63.85   $63.85   $63.80  
  7 purchase totals = $839.43       $881.3227   $881.33   $881.30   $881.20