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 $54.56   11.362%   $60.7591   $60.76   $60.75   $60.80  
  Purchase #2 $142.38   9.657%   $156.1296   $156.13   $156.15   $156.10  
  Purchase #3 $119.50   6.740%   $127.5543   $127.55   $127.55   $127.60  
  Purchase #4 $142.98   8.480%   $155.1047   $155.10   $155.10   $155.10  
  Purchase #5 $192.36   8.665%   $209.028   $209.03   $209.05   $209.00  
  Purchase #6 $233.79   8.794%   $254.3495   $254.35   $254.35   $254.30  
  Purchase #7 $143.55   12.284%   $161.1837   $161.18   $161.20   $161.20  
  7 purchase totals = $1,029.12       $1,124.1089   $1,124.10   $1,124.15   $1,124.10