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 $203.61   11.487%   $226.9987   $227.00   $227.00   $227.00  
  Purchase #2 $98.39   12.790%   $110.9741   $110.97   $110.95   $111.00  
  Purchase #3 $101.43   7.772%   $109.3131   $109.31   $109.30   $109.30  
  Purchase #4 $159.77   10.216%   $176.0921   $176.09   $176.10   $176.10  
  Purchase #5 $76.74   6.359%   $81.6199   $81.62   $81.60   $81.60  
  Purchase #6 $219.38   5.787%   $232.0755   $232.08   $232.10   $232.10  
  Purchase #7 $208.81   6.298%   $221.9609   $221.96   $221.95   $222.00  
  7 purchase totals = $1,068.13       $1,159.0343   $1,159.03   $1,159.00   $1,159.10