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 $206.79   9.873%   $227.2064   $227.21   $227.20   $227.20  
  Purchase #2 $249.35   8.830%   $271.3676   $271.37   $271.35   $271.40  
  Purchase #3 $66.75   3.818%   $69.2985   $69.30   $69.30   $69.30  
  Purchase #4 $61.56   13.836%   $70.0774   $70.08   $70.10   $70.10  
  Purchase #5 $94.48   9.661%   $103.6077   $103.61   $103.60   $103.60  
  Purchase #6 $9.43   5.659%   $9.9636   $9.96   $9.95   $10.00  
  Purchase #7 $147.79   11.729%   $165.1243   $165.12   $165.10   $165.10  
  7 purchase totals = $836.15       $916.6455   $916.65   $916.60   $916.70