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 $224.77   10.152%   $247.5887   $247.59   $247.60   $247.60  
  Purchase #2 $236.77   12.758%   $266.9771   $266.98   $267.00   $267.00  
  Purchase #3 $158.28   9.168%   $172.7911   $172.79   $172.80   $172.80  
  Purchase #4 $226.74   12.777%   $255.7106   $255.71   $255.70   $255.70  
  Purchase #5 $229.38   10.623%   $253.747   $253.75   $253.75   $253.70  
  Purchase #6 $195.57   4.825%   $205.0063   $205.01   $205.00   $205.00  
  Purchase #7 $24.45   13.187%   $27.6742   $27.67   $27.65   $27.70  
  7 purchase totals = $1,295.96       $1,429.4950   $1,429.50   $1,429.50   $1,429.50