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 $95.36   3.655%   $98.8454   $98.85   $98.85   $98.80  
  Purchase #2 $169.55   7.476%   $182.2256   $182.23   $182.25   $182.20  
  Purchase #3 $221.60   3.192%   $228.6735   $228.67   $228.65   $228.70  
  Purchase #4 $233.46   11.347%   $259.9507   $259.95   $259.95   $260.00  
  Purchase #5 $87.83   6.359%   $93.4151   $93.42   $93.40   $93.40  
  Purchase #6 $69.50   5.306%   $73.1877   $73.19   $73.20   $73.20  
  Purchase #7 $103.45   9.474%   $113.2509   $113.25   $113.25   $113.30  
  7 purchase totals = $980.75       $1,049.5489   $1,049.56   $1,049.55   $1,049.60