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 $118.94   11.872%   $133.0606   $133.06   $133.05   $133.10  
  Purchase #2 $145.97   6.219%   $155.0479   $155.05   $155.05   $155.00  
  Purchase #3 $9.83   5.295%   $10.3505   $10.35   $10.35   $10.40  
  Purchase #4 $88.33   6.322%   $93.9142   $93.91   $93.90   $93.90  
  Purchase #5 $112.77   7.251%   $120.947   $120.95   $120.95   $120.90  
  Purchase #6 $191.94   13.279%   $217.4277   $217.43   $217.45   $217.40  
  Purchase #7 $56.29   6.663%   $60.0406   $60.04   $60.05   $60.00  
  7 purchase totals = $724.07       $790.7885   $790.79   $790.80   $790.70