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 $118.65   10.425%   $131.0193   $131.02   $131.00   $131.00  
  Purchase #2 $240.47   10.832%   $266.5177   $266.52   $266.50   $266.50  
  Purchase #3 $213.34   11.778%   $238.4672   $238.47   $238.45   $238.50  
  Purchase #4 $29.43   10.707%   $32.5811   $32.58   $32.60   $32.60  
  Purchase #5 $169.39   13.782%   $192.7353   $192.74   $192.75   $192.70  
  Purchase #6 $14.77   8.314%   $15.998   $16.00   $16.00   $16.00  
  Purchase #7 $64.57   3.343%   $66.7286   $66.73   $66.75   $66.70  
  7 purchase totals = $850.62       $944.0472   $944.06   $944.05   $944.00