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 $39.89   11.597%   $44.516   $44.52   $44.50   $44.50  
  Purchase #2 $31.54   7.630%   $33.9465   $33.95   $33.95   $33.90  
  Purchase #3 $30.29   12.178%   $33.9787   $33.98   $34.00   $34.00  
  Purchase #4 $233.46   7.647%   $251.3127   $251.31   $251.30   $251.30  
  Purchase #5 $127.67   3.775%   $132.4895   $132.49   $132.50   $132.50  
  Purchase #6 $64.74   13.798%   $73.6728   $73.67   $73.65   $73.70  
  Purchase #7 $186.33   9.130%   $203.3419   $203.34   $203.35   $203.30  
  7 purchase totals = $713.92       $773.2581   $773.26   $773.25   $773.20