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 $58.61   11.463%   $65.3285   $65.33   $65.35   $65.30  
  Purchase #2 $22.31   11.838%   $24.9511   $24.95   $24.95   $25.00  
  Purchase #3 $191.98   11.329%   $213.7294   $213.73   $213.75   $213.70  
  Purchase #4 $216.44   9.352%   $236.6815   $236.68   $236.70   $236.70  
  Purchase #5 $153.80   13.650%   $174.7937   $174.79   $174.80   $174.80  
  Purchase #6 $198.48   10.490%   $219.3006   $219.30   $219.30   $219.30  
  Purchase #7 $12.98   6.655%   $13.8438   $13.84   $13.85   $13.80  
  7 purchase totals = $854.60       $948.6286   $948.62   $948.70   $948.60