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 $61.59   6.330%   $65.4886   $65.49   $65.50   $65.50  
  Purchase #2 $51.88   11.773%   $57.9878   $57.99   $58.00   $58.00  
  Purchase #3 $121.97   7.445%   $131.0507   $131.05   $131.05   $131.10  
  Purchase #4 $204.47   3.117%   $210.8433   $210.84   $210.85   $210.80  
  Purchase #5 $155.35   13.611%   $176.4947   $176.49   $176.50   $176.50  
  Purchase #6 $128.25   11.143%   $142.5409   $142.54   $142.55   $142.50  
  Purchase #7 $166.55   6.714%   $177.7322   $177.73   $177.75   $177.70  
  7 purchase totals = $890.06       $962.1382   $962.13   $962.20   $962.10