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 $34.87   6.792%   $37.2384   $37.24   $37.25   $37.20  
  Purchase #2 $74.81   9.424%   $81.8601   $81.86   $81.85   $81.90  
  Purchase #3 $15.91   5.728%   $16.8213   $16.82   $16.80   $16.80  
  Purchase #4 $173.32   12.457%   $194.9105   $194.91   $194.90   $194.90  
  Purchase #5 $49.79   9.112%   $54.3269   $54.33   $54.35   $54.30  
  Purchase #6 $194.57   5.747%   $205.7519   $205.75   $205.75   $205.80  
  Purchase #7 $208.75   11.837%   $233.4597   $233.46   $233.45   $233.50  
  7 purchase totals = $752.02       $824.3688   $824.37   $824.35   $824.40