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 $202.86   4.757%   $212.5101   $212.51   $212.50   $212.50  
  Purchase #2 $84.98   5.149%   $89.3556   $89.36   $89.35   $89.40  
  Purchase #3 $63.79   13.814%   $72.602   $72.60   $72.60   $72.60  
  Purchase #4 $247.89   5.281%   $260.9811   $260.98   $261.00   $261.00  
  Purchase #5 $141.31   6.788%   $150.9021   $150.90   $150.90   $150.90  
  Purchase #6 $180.88   7.245%   $193.9848   $193.98   $194.00   $194.00  
  Purchase #7 $149.39   7.775%   $161.0051   $161.01   $161.00   $161.00  
  7 purchase totals = $1,071.10       $1,141.3408   $1,141.34   $1,141.35   $1,141.40