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 $89.54   8.620%   $97.2583   $97.26   $97.25   $97.30  
  Purchase #2 $55.97   4.681%   $58.59   $58.59   $58.60   $58.60  
  Purchase #3 $237.92   11.815%   $266.0302   $266.03   $266.05   $266.00  
  Purchase #4 $237.47   11.205%   $264.0785   $264.08   $264.10   $264.10  
  Purchase #5 $17.75   12.766%   $20.016   $20.02   $20.00   $20.00  
  Purchase #6 $223.99   10.216%   $246.8728   $246.87   $246.85   $246.90  
  Purchase #7 $157.84   6.387%   $167.9212   $167.92   $167.90   $167.90  
  7 purchase totals = $1,020.48       $1,120.7670   $1,120.77   $1,120.75   $1,120.80