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 $137.71   9.159%   $150.3229   $150.32   $150.30   $150.30  
  Purchase #2 $73.30   5.364%   $77.2318   $77.23   $77.25   $77.20  
  Purchase #3 $86.99   11.510%   $97.0025   $97.00   $97.00   $97.00  
  Purchase #4 $5.72   12.617%   $6.4417   $6.44   $6.45   $6.40  
  Purchase #5 $91.65   12.163%   $102.7974   $102.80   $102.80   $102.80  
  Purchase #6 $118.95   13.693%   $135.2378   $135.24   $135.25   $135.20  
  Purchase #7 $144.64   3.513%   $149.7212   $149.72   $149.70   $149.70  
  7 purchase totals = $658.96       $718.7553   $718.75   $718.75   $718.60