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 $195.44   8.346%   $211.7514   $211.75   $211.75   $211.80  
  Purchase #2 $174.25   9.747%   $191.2341   $191.23   $191.25   $191.20  
  Purchase #3 $163.75   11.591%   $182.7303   $182.73   $182.75   $182.70  
  Purchase #4 $227.74   5.423%   $240.0903   $240.09   $240.10   $240.10  
  Purchase #5 $58.70   3.802%   $60.9318   $60.93   $60.95   $60.90  
  Purchase #6 $128.55   13.469%   $145.8644   $145.86   $145.85   $145.90  
  Purchase #7 $50.68   5.494%   $53.4644   $53.46   $53.45   $53.50  
  7 purchase totals = $999.11       $1,086.0667   $1,086.05   $1,086.10   $1,086.10