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 $86.35   13.463%   $97.9753   $97.98   $98.00   $98.00  
  Purchase #2 $206.72   6.225%   $219.5883   $219.59   $219.60   $219.60  
  Purchase #3 $66.82   4.740%   $69.9873   $69.99   $70.00   $70.00  
  Purchase #4 $234.86   7.795%   $253.1673   $253.17   $253.15   $253.20  
  Purchase #5 $101.28   9.781%   $111.1862   $111.19   $111.20   $111.20  
  Purchase #6 $131.92   10.555%   $145.8442   $145.84   $145.85   $145.80  
  Purchase #7 $111.80   6.596%   $119.1743   $119.17   $119.15   $119.20  
  7 purchase totals = $939.75       $1,016.9229   $1,016.93   $1,016.95   $1,017.00