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 $144.99   4.674%   $151.7668   $151.77   $151.75   $151.80  
  Purchase #2 $220.65   12.850%   $249.0035   $249.00   $249.00   $249.00  
  Purchase #3 $56.92   6.327%   $60.5213   $60.52   $60.50   $60.50  
  Purchase #4 $140.83   4.302%   $146.8885   $146.89   $146.90   $146.90  
  Purchase #5 $116.33   9.843%   $127.7804   $127.78   $127.80   $127.80  
  Purchase #6 $91.50   5.389%   $96.4309   $96.43   $96.45   $96.40  
  Purchase #7 $155.82   12.416%   $175.1666   $175.17   $175.15   $175.20  
  7 purchase totals = $927.04       $1,007.5580   $1,007.56   $1,007.55   $1,007.60