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 $82.97   12.614%   $93.4358   $93.44   $93.45   $93.40  
  Purchase #2 $144.34   8.232%   $156.2221   $156.22   $156.20   $156.20  
  Purchase #3 $228.34   7.765%   $246.0706   $246.07   $246.05   $246.10  
  Purchase #4 $170.37   6.674%   $181.7405   $181.74   $181.75   $181.70  
  Purchase #5 $127.65   11.843%   $142.7676   $142.77   $142.75   $142.80  
  Purchase #6 $135.32   11.835%   $151.3351   $151.34   $151.35   $151.30  
  Purchase #7 $54.35   10.719%   $60.1758   $60.18   $60.20   $60.20  
  7 purchase totals = $943.34       $1,031.7475   $1,031.76   $1,031.75   $1,031.70