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 $110.54   13.768%   $125.7591   $125.76   $125.75   $125.80  
  Purchase #2 $58.65   12.426%   $65.9378   $65.94   $65.95   $65.90  
  Purchase #3 $237.70   11.392%   $264.7788   $264.78   $264.80   $264.80  
  Purchase #4 $124.36   5.607%   $131.3329   $131.33   $131.35   $131.30  
  Purchase #5 $187.96   8.691%   $204.2956   $204.30   $204.30   $204.30  
  Purchase #6 $156.88   9.615%   $171.964   $171.96   $171.95   $172.00  
  Purchase #7 $69.38   5.324%   $73.0738   $73.07   $73.05   $73.10  
  7 purchase totals = $945.47       $1,037.1420   $1,037.14   $1,037.15   $1,037.20