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 $167.96   5.407%   $177.0416   $177.04   $177.05   $177.00  
  Purchase #2 $54.86   7.359%   $58.8971   $58.90   $58.90   $58.90  
  Purchase #3 $181.99   11.327%   $202.604   $202.60   $202.60   $202.60  
  Purchase #4 $8.27   3.753%   $8.5804   $8.58   $8.60   $8.60  
  Purchase #5 $97.86   9.318%   $106.9786   $106.98   $107.00   $107.00  
  Purchase #6 $174.30   10.672%   $192.9013   $192.90   $192.90   $192.90  
  Purchase #7 $13.69   6.730%   $14.6113   $14.61   $14.60   $14.60  
  7 purchase totals = $698.93       $761.6143   $761.61   $761.65   $761.60