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 $61.99   11.621%   $69.1939   $69.19   $69.20   $69.20  
  Purchase #2 $22.67   6.370%   $24.1141   $24.11   $24.10   $24.10  
  Purchase #3 $143.94   10.435%   $158.9601   $158.96   $158.95   $159.00  
  Purchase #4 $219.34   9.123%   $239.3504   $239.35   $239.35   $239.40  
  Purchase #5 $218.38   12.859%   $246.4615   $246.46   $246.45   $246.50  
  Purchase #6 $74.56   6.227%   $79.2029   $79.20   $79.20   $79.20  
  Purchase #7 $33.49   9.855%   $36.7904   $36.79   $36.80   $36.80  
  7 purchase totals = $774.37       $854.0733   $854.06   $854.05   $854.20