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 $158.78   5.618%   $167.7003   $167.70   $167.70   $167.70  
  Purchase #2 $136.30   6.307%   $144.8964   $144.90   $144.90   $144.90  
  Purchase #3 $107.93   8.146%   $116.722   $116.72   $116.70   $116.70  
  Purchase #4 $181.96   13.311%   $206.1807   $206.18   $206.20   $206.20  
  Purchase #5 $224.33   5.355%   $236.3429   $236.34   $236.35   $236.30  
  Purchase #6 $201.96   13.387%   $228.9964   $229.00   $229.00   $229.00  
  Purchase #7 $82.88   13.511%   $94.0779   $94.08   $94.10   $94.10  
  7 purchase totals = $1,094.14       $1,194.9166   $1,194.92   $1,194.95   $1,194.90