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 $59.47   11.872%   $66.5303   $66.53   $66.55   $66.50  
  Purchase #2 $208.68   11.626%   $232.9411   $232.94   $232.95   $232.90  
  Purchase #3 $132.49   9.341%   $144.8659   $144.87   $144.85   $144.90  
  Purchase #4 $245.33   5.480%   $258.7741   $258.77   $258.75   $258.80  
  Purchase #5 $44.29   9.803%   $48.6317   $48.63   $48.65   $48.60  
  Purchase #6 $133.50   8.270%   $144.5405   $144.54   $144.55   $144.50  
  Purchase #7 $145.70   6.716%   $155.4852   $155.49   $155.50   $155.50  
  7 purchase totals = $969.46       $1,051.7688   $1,051.77   $1,051.80   $1,051.70