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 $58.42   6.503%   $62.2191   $62.22   $62.20   $62.20  
  Purchase #2 $202.41   7.692%   $217.9794   $217.98   $218.00   $218.00  
  Purchase #3 $132.93   7.565%   $142.9862   $142.99   $143.00   $143.00  
  Purchase #4 $46.49   10.357%   $51.305   $51.31   $51.30   $51.30  
  Purchase #5 $80.81   11.184%   $89.8478   $89.85   $89.85   $89.80  
  Purchase #6 $153.33   6.437%   $163.1999   $163.20   $163.20   $163.20  
  Purchase #7 $207.33   9.252%   $226.5122   $226.51   $226.50   $226.50  
  7 purchase totals = $881.72       $954.0496   $954.06   $954.05   $954.00