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 $219.51   6.647%   $234.1008   $234.10   $234.10   $234.10  
  Purchase #2 $124.61   11.496%   $138.9352   $138.94   $138.95   $138.90  
  Purchase #3 $223.94   12.660%   $252.2908   $252.29   $252.30   $252.30  
  Purchase #4 $38.79   7.859%   $41.8385   $41.84   $41.85   $41.80  
  Purchase #5 $188.77   6.204%   $200.4813   $200.48   $200.50   $200.50  
  Purchase #6 $192.90   6.213%   $204.8849   $204.88   $204.90   $204.90  
  Purchase #7 $54.78   10.660%   $60.6195   $60.62   $60.60   $60.60  
  7 purchase totals = $1,043.30       $1,133.1510   $1,133.15   $1,133.20   $1,133.10