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 $242.51   4.518%   $253.4666   $253.47   $253.45   $253.50  
  Purchase #2 $209.29   8.302%   $226.6653   $226.67   $226.65   $226.70  
  Purchase #3 $30.97   7.830%   $33.395   $33.40   $33.40   $33.40  
  Purchase #4 $102.39   10.868%   $113.5177   $113.52   $113.50   $113.50  
  Purchase #5 $99.75   7.302%   $107.0337   $107.03   $107.05   $107.00  
  Purchase #6 $221.78   6.702%   $236.6437   $236.64   $236.65   $236.60  
  Purchase #7 $78.95   13.320%   $89.4661   $89.47   $89.45   $89.50  
  7 purchase totals = $985.64       $1,060.1881   $1,060.20   $1,060.15   $1,060.20