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 $60.28   11.174%   $67.0157   $67.02   $67.00   $67.00  
  Purchase #2 $223.79   8.323%   $242.416   $242.42   $242.40   $242.40  
  Purchase #3 $160.60   12.465%   $180.6188   $180.62   $180.60   $180.60  
  Purchase #4 $110.99   13.442%   $125.9093   $125.91   $125.90   $125.90  
  Purchase #5 $10.79   13.289%   $12.2239   $12.22   $12.20   $12.20  
  Purchase #6 $78.64   9.632%   $86.2146   $86.21   $86.20   $86.20  
  Purchase #7 $29.75   11.454%   $33.1576   $33.16   $33.15   $33.20  
  7 purchase totals = $674.84       $747.5559   $747.56   $747.45   $747.50