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 $67.96   10.657%   $75.2025   $75.20   $75.20   $75.20  
  Purchase #2 $83.42   5.792%   $88.2517   $88.25   $88.25   $88.30  
  Purchase #3 $137.84   11.843%   $154.1644   $154.16   $154.15   $154.20  
  Purchase #4 $208.70   5.167%   $219.4835   $219.48   $219.50   $219.50  
  Purchase #5 $198.34   6.593%   $211.4166   $211.42   $211.40   $211.40  
  Purchase #6 $89.91   13.664%   $102.1953   $102.20   $102.20   $102.20  
  Purchase #7 $194.77   9.148%   $212.5876   $212.59   $212.60   $212.60  
  7 purchase totals = $980.94       $1,063.3016   $1,063.30   $1,063.30   $1,063.40