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 $60.49   7.476%   $65.0122   $65.01   $65.00   $65.00  
  Purchase #2 $23.34   6.203%   $24.7878   $24.79   $24.80   $24.80  
  Purchase #3 $67.60   12.661%   $76.1588   $76.16   $76.15   $76.20  
  Purchase #4 $67.97   4.252%   $70.8601   $70.86   $70.85   $70.90  
  Purchase #5 $183.69   4.465%   $191.8918   $191.89   $191.90   $191.90  
  Purchase #6 $204.55   13.692%   $232.557   $232.56   $232.55   $232.60  
  Purchase #7 $174.90   9.504%   $191.5225   $191.52   $191.50   $191.50  
  7 purchase totals = $782.54       $852.7902   $852.79   $852.75   $852.90