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 $54.97   5.440%   $57.9604   $57.96   $57.95   $58.00  
  Purchase #2 $228.56   6.550%   $243.5307   $243.53   $243.55   $243.50  
  Purchase #3 $175.36   9.731%   $192.4243   $192.42   $192.40   $192.40  
  Purchase #4 $226.43   3.545%   $234.4569   $234.46   $234.45   $234.50  
  Purchase #5 $133.94   13.110%   $151.4995   $151.50   $151.50   $151.50  
  Purchase #6 $221.41   6.103%   $234.9227   $234.92   $234.90   $234.90  
  Purchase #7 $108.84   6.531%   $115.9483   $115.95   $115.95   $115.90  
  7 purchase totals = $1,149.51       $1,230.7428   $1,230.74   $1,230.70   $1,230.70