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 $86.27   9.338%   $94.3259   $94.33   $94.35   $94.30  
  Purchase #2 $81.95   11.610%   $91.4644   $91.46   $91.45   $91.50  
  Purchase #3 $43.77   12.831%   $49.3861   $49.39   $49.40   $49.40  
  Purchase #4 $184.37   9.537%   $201.9534   $201.95   $201.95   $202.00  
  Purchase #5 $226.73   13.435%   $257.1912   $257.19   $257.20   $257.20  
  Purchase #6 $8.91   11.760%   $9.9578   $9.96   $9.95   $10.00  
  Purchase #7 $65.73   4.574%   $68.7365   $68.74   $68.75   $68.70  
  7 purchase totals = $697.73       $773.0153   $773.02   $773.05   $773.10