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 $49.48   6.501%   $52.6967   $52.70   $52.70   $52.70  
  Purchase #2 $107.68   9.500%   $117.9096   $117.91   $117.90   $117.90  
  Purchase #3 $62.46   7.763%   $67.3088   $67.31   $67.30   $67.30  
  Purchase #4 $53.95   12.485%   $60.6857   $60.69   $60.70   $60.70  
  Purchase #5 $57.31   9.184%   $62.5734   $62.57   $62.55   $62.60  
  Purchase #6 $204.81   6.587%   $218.3008   $218.30   $218.30   $218.30  
  Purchase #7 $139.31   4.191%   $145.1485   $145.15   $145.15   $145.10  
  7 purchase totals = $675.00       $724.6235   $724.63   $724.60   $724.60