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 $95.86   6.652%   $102.2366   $102.24   $102.25   $102.20  
  Purchase #2 $250.70   9.419%   $274.3134   $274.31   $274.30   $274.30  
  Purchase #3 $28.52   5.323%   $30.0381   $30.04   $30.05   $30.00  
  Purchase #4 $136.27   4.222%   $142.0233   $142.02   $142.00   $142.00  
  Purchase #5 $17.93   4.153%   $18.6746   $18.67   $18.65   $18.70  
  Purchase #6 $219.45   6.268%   $233.2051   $233.21   $233.20   $233.20  
  Purchase #7 $24.36   4.197%   $25.3824   $25.38   $25.40   $25.40  
  7 purchase totals = $773.09       $825.8735   $825.87   $825.85   $825.80