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 $192.86   6.108%   $204.6399   $204.64   $204.65   $204.60  
  Purchase #2 $221.33   6.438%   $235.5792   $235.58   $235.60   $235.60  
  Purchase #3 $116.57   10.569%   $128.8903   $128.89   $128.90   $128.90  
  Purchase #4 $103.57   5.132%   $108.8852   $108.89   $108.90   $108.90  
  Purchase #5 $23.92   12.341%   $26.872   $26.87   $26.85   $26.90  
  Purchase #6 $173.73   11.103%   $193.0192   $193.02   $193.00   $193.00  
  Purchase #7 $163.31   12.287%   $183.3759   $183.38   $183.40   $183.40  
  7 purchase totals = $995.29       $1,081.2617   $1,081.27   $1,081.30   $1,081.30