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 $184.82   12.419%   $207.7728   $207.77   $207.75   $207.80  
  Purchase #2 $191.72   9.718%   $210.3513   $210.35   $210.35   $210.40  
  Purchase #3 $206.59   11.219%   $229.7673   $229.77   $229.75   $229.80  
  Purchase #4 $29.71   8.136%   $32.1272   $32.13   $32.15   $32.10  
  Purchase #5 $141.64   13.142%   $160.2543   $160.25   $160.25   $160.30  
  Purchase #6 $150.62   3.251%   $155.5167   $155.52   $155.50   $155.50  
  Purchase #7 $246.69   10.847%   $273.4485   $273.45   $273.45   $273.40  
  7 purchase totals = $1,151.79       $1,269.2381   $1,269.24   $1,269.20   $1,269.30