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 $60.72   8.197%   $65.6972   $65.70   $65.70   $65.70  
  Purchase #2 $98.37   4.679%   $102.9727   $102.97   $102.95   $103.00  
  Purchase #3 $142.32   12.765%   $160.4871   $160.49   $160.50   $160.50  
  Purchase #4 $97.43   10.339%   $107.5033   $107.50   $107.50   $107.50  
  Purchase #5 $240.34   11.244%   $267.3638   $267.36   $267.35   $267.40  
  Purchase #6 $24.32   9.358%   $26.5959   $26.60   $26.60   $26.60  
  Purchase #7 $191.96   10.543%   $212.1983   $212.20   $212.20   $212.20  
  7 purchase totals = $855.46       $942.8183   $942.82   $942.80   $942.90