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 $168.92   8.230%   $182.8221   $182.82   $182.80   $182.80  
  Purchase #2 $230.59   10.729%   $255.33   $255.33   $255.35   $255.30  
  Purchase #3 $209.41   8.548%   $227.3104   $227.31   $227.30   $227.30  
  Purchase #4 $144.65   7.326%   $155.2471   $155.25   $155.25   $155.20  
  Purchase #5 $212.95   7.557%   $229.0426   $229.04   $229.05   $229.00  
  Purchase #6 $168.95   5.461%   $178.1764   $178.18   $178.20   $178.20  
  Purchase #7 $117.40   12.270%   $131.805   $131.81   $131.80   $131.80  
  7 purchase totals = $1,252.87       $1,359.7336   $1,359.74   $1,359.75   $1,359.60