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 $244.71   12.623%   $275.5997   $275.60   $275.60   $275.60  
  Purchase #2 $77.86   10.143%   $85.7573   $85.76   $85.75   $85.80  
  Purchase #3 $114.84   11.739%   $128.3211   $128.32   $128.30   $128.30  
  Purchase #4 $15.33   10.533%   $16.9447   $16.94   $16.95   $16.90  
  Purchase #5 $82.47   13.570%   $93.6612   $93.66   $93.65   $93.70  
  Purchase #6 $93.85   13.871%   $106.8679   $106.87   $106.85   $106.90  
  Purchase #7 $59.87   4.500%   $62.5642   $62.56   $62.55   $62.60  
  7 purchase totals = $688.93       $769.7161   $769.71   $769.65   $769.80