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 $130.39   11.424%   $145.2858   $145.29   $145.30   $145.30  
  Purchase #2 $234.67   12.508%   $264.0225   $264.02   $264.00   $264.00  
  Purchase #3 $76.78   11.533%   $85.635   $85.64   $85.65   $85.60  
  Purchase #4 $54.70   10.346%   $60.3593   $60.36   $60.35   $60.40  
  Purchase #5 $56.73   6.283%   $60.2943   $60.29   $60.30   $60.30  
  Purchase #6 $101.86   6.237%   $108.213   $108.21   $108.20   $108.20  
  Purchase #7 $244.98   12.175%   $274.8063   $274.81   $274.80   $274.80  
  7 purchase totals = $900.11       $998.6162   $998.62   $998.60   $998.60