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 $244.77   12.849%   $276.2205   $276.22   $276.20   $276.20  
  Purchase #2 $125.95   13.274%   $142.6686   $142.67   $142.65   $142.70  
  Purchase #3 $108.94   3.555%   $112.8128   $112.81   $112.80   $112.80  
  Purchase #4 $159.99   11.858%   $178.9616   $178.96   $178.95   $179.00  
  Purchase #5 $223.31   5.456%   $235.4938   $235.49   $235.50   $235.50  
  Purchase #6 $66.68   13.454%   $75.6511   $75.65   $75.65   $75.70  
  Purchase #7 $178.60   13.723%   $203.1093   $203.11   $203.10   $203.10  
  7 purchase totals = $1,108.24       $1,224.9177   $1,224.91   $1,224.85   $1,225.00