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 $60.87   3.633%   $63.0814   $63.08   $63.10   $63.10  
  Purchase #2 $50.66   10.490%   $55.9742   $55.97   $55.95   $56.00  
  Purchase #3 $121.25   4.769%   $127.0324   $127.03   $127.05   $127.00  
  Purchase #4 $24.31   4.580%   $25.4234   $25.42   $25.40   $25.40  
  Purchase #5 $212.27   12.219%   $238.2073   $238.21   $238.20   $238.20  
  Purchase #6 $66.82   13.746%   $76.0051   $76.01   $76.00   $76.00  
  Purchase #7 $187.34   5.515%   $197.6718   $197.67   $197.65   $197.70  
  7 purchase totals = $723.52       $783.3956   $783.39   $783.35   $783.40