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 $247.69   11.852%   $277.0462   $277.05   $277.05   $277.00  
  Purchase #2 $230.73   9.654%   $253.0047   $253.00   $253.00   $253.00  
  Purchase #3 $142.70   5.172%   $150.0804   $150.08   $150.10   $150.10  
  Purchase #4 $230.94   12.276%   $259.2902   $259.29   $259.30   $259.30  
  Purchase #5 $236.78   3.217%   $244.3972   $244.40   $244.40   $244.40  
  Purchase #6 $101.25   8.800%   $110.16   $110.16   $110.15   $110.20  
  Purchase #7 $138.28   8.564%   $150.1223   $150.12   $150.10   $150.10  
  7 purchase totals = $1,328.37       $1,444.1010   $1,444.10   $1,444.10   $1,444.10