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 $55.67   12.258%   $62.494   $62.49   $62.50   $62.50  
  Purchase #2 $152.36   11.145%   $169.3405   $169.34   $169.35   $169.30  
  Purchase #3 $96.25   3.435%   $99.5562   $99.56   $99.55   $99.60  
  Purchase #4 $217.60   6.786%   $232.3663   $232.37   $232.35   $232.40  
  Purchase #5 $42.54   10.442%   $46.982   $46.98   $47.00   $47.00  
  Purchase #6 $26.68   12.330%   $29.9696   $29.97   $29.95   $30.00  
  Purchase #7 $225.32   6.455%   $239.8644   $239.86   $239.85   $239.90  
  7 purchase totals = $816.42       $880.5730   $880.57   $880.55   $880.70