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 $243.47   8.852%   $265.022   $265.02   $265.00   $265.00  
  Purchase #2 $138.56   12.768%   $156.2513   $156.25   $156.25   $156.30  
  Purchase #3 $207.35   12.246%   $232.7421   $232.74   $232.75   $232.70  
  Purchase #4 $83.42   11.289%   $92.8373   $92.84   $92.85   $92.80  
  Purchase #5 $33.68   4.762%   $35.2838   $35.28   $35.30   $35.30  
  Purchase #6 $150.51   12.141%   $168.7834   $168.78   $168.80   $168.80  
  Purchase #7 $88.80   8.726%   $96.5487   $96.55   $96.55   $96.50  
  7 purchase totals = $945.79       $1,047.4686   $1,047.46   $1,047.50   $1,047.40