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 $58.62   8.316%   $63.4948   $63.49   $63.50   $63.50  
  Purchase #2 $63.54   12.764%   $71.6502   $71.65   $71.65   $71.70  
  Purchase #3 $135.57   12.842%   $152.9799   $152.98   $153.00   $153.00  
  Purchase #4 $124.47   6.228%   $132.222   $132.22   $132.20   $132.20  
  Purchase #5 $168.89   7.604%   $181.7324   $181.73   $181.75   $181.70  
  Purchase #6 $161.33   13.185%   $182.6014   $182.60   $182.60   $182.60  
  Purchase #7 $8.45   8.242%   $9.1464   $9.15   $9.15   $9.10  
  7 purchase totals = $720.87       $793.8271   $793.82   $793.85   $793.80