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 $91.64   13.262%   $103.7933   $103.79   $103.80   $103.80  
  Purchase #2 $157.48   13.441%   $178.6469   $178.65   $178.65   $178.60  
  Purchase #3 $68.77   12.258%   $77.1998   $77.20   $77.20   $77.20  
  Purchase #4 $225.87   5.375%   $238.0105   $238.01   $238.00   $238.00  
  Purchase #5 $63.88   13.700%   $72.6316   $72.63   $72.65   $72.60  
  Purchase #6 $7.65   10.467%   $8.4507   $8.45   $8.45   $8.50  
  Purchase #7 $195.72   3.711%   $202.9832   $202.98   $203.00   $203.00  
  7 purchase totals = $811.01       $881.7160   $881.71   $881.75   $881.70