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 $92.74   12.781%   $104.5931   $104.59   $104.60   $104.60  
  Purchase #2 $113.81   11.738%   $127.169   $127.17   $127.15   $127.20  
  Purchase #3 $65.47   4.623%   $68.4967   $68.50   $68.50   $68.50  
  Purchase #4 $166.53   9.726%   $182.7267   $182.73   $182.75   $182.70  
  Purchase #5 $206.60   13.264%   $234.0034   $234.00   $234.00   $234.00  
  Purchase #6 $218.88   6.190%   $232.4287   $232.43   $232.45   $232.40  
  Purchase #7 $113.81   10.150%   $125.3617   $125.36   $125.35   $125.40  
  7 purchase totals = $977.84       $1,074.7793   $1,074.78   $1,074.80   $1,074.80