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 $51.93   5.234%   $54.648   $54.65   $54.65   $54.60  
  Purchase #2 $152.31   4.222%   $158.7405   $158.74   $158.75   $158.70  
  Purchase #3 $222.65   8.772%   $242.1809   $242.18   $242.20   $242.20  
  Purchase #4 $73.50   5.674%   $77.6704   $77.67   $77.65   $77.70  
  Purchase #5 $75.25   5.681%   $79.525   $79.53   $79.55   $79.50  
  Purchase #6 $103.27   11.591%   $115.24   $115.24   $115.25   $115.20  
  Purchase #7 $246.31   5.621%   $260.1551   $260.16   $260.15   $260.20  
  7 purchase totals = $925.22       $988.1599   $988.17   $988.20   $988.10