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 $40.62   13.197%   $45.9806   $45.98   $46.00   $46.00  
  Purchase #2 $120.30   10.264%   $132.6476   $132.65   $132.65   $132.60  
  Purchase #3 $44.47   11.761%   $49.7001   $49.70   $49.70   $49.70  
  Purchase #4 $17.84   11.294%   $19.8548   $19.85   $19.85   $19.90  
  Purchase #5 $50.39   6.365%   $53.5973   $53.60   $53.60   $53.60  
  Purchase #6 $239.38   6.398%   $254.6955   $254.70   $254.70   $254.70  
  Purchase #7 $235.59   11.471%   $262.6145   $262.61   $262.60   $262.60  
  7 purchase totals = $748.59       $819.0904   $819.09   $819.10   $819.10