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 $243.66   8.748%   $264.9754   $264.98   $265.00   $265.00  
  Purchase #2 $244.70   4.807%   $256.4627   $256.46   $256.45   $256.50  
  Purchase #3 $103.25   6.214%   $109.666   $109.67   $109.65   $109.70  
  Purchase #4 $35.55   3.232%   $36.699   $36.70   $36.70   $36.70  
  Purchase #5 $151.97   5.661%   $160.573   $160.57   $160.55   $160.60  
  Purchase #6 $84.52   12.600%   $95.1695   $95.17   $95.15   $95.20  
  Purchase #7 $86.82   12.729%   $97.8713   $97.87   $97.85   $97.90  
  7 purchase totals = $950.47       $1,021.4169   $1,021.42   $1,021.35   $1,021.60