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 $168.75   4.862%   $176.9546   $176.95   $176.95   $177.00  
  Purchase #2 $241.67   7.312%   $259.3409   $259.34   $259.35   $259.30  
  Purchase #3 $200.58   11.857%   $224.3628   $224.36   $224.35   $224.40  
  Purchase #4 $247.91   11.664%   $276.8262   $276.83   $276.85   $276.80  
  Purchase #5 $50.52   7.412%   $54.2645   $54.26   $54.25   $54.30  
  Purchase #6 $197.75   6.873%   $211.3414   $211.34   $211.35   $211.30  
  Purchase #7 $19.49   7.817%   $21.0135   $21.01   $21.00   $21.00  
  7 purchase totals = $1,126.67       $1,224.1039   $1,224.09   $1,224.10   $1,224.10