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 $214.97   10.258%   $237.0216   $237.02   $237.00   $237.00  
  Purchase #2 $203.43   12.648%   $229.1598   $229.16   $229.15   $229.20  
  Purchase #3 $23.65   5.363%   $24.9183   $24.92   $24.90   $24.90  
  Purchase #4 $47.85   4.561%   $50.0324   $50.03   $50.05   $50.00  
  Purchase #5 $84.80   4.721%   $88.8034   $88.80   $88.80   $88.80  
  Purchase #6 $234.73   4.763%   $245.9102   $245.91   $245.90   $245.90  
  Purchase #7 $38.95   11.273%   $43.3408   $43.34   $43.35   $43.30  
  7 purchase totals = $848.38       $919.1865   $919.18   $919.15   $919.10