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 $62.36   9.607%   $68.3509   $68.35   $68.35   $68.40  
  Purchase #2 $24.68   8.839%   $26.8615   $26.86   $26.85   $26.90  
  Purchase #3 $196.28   6.543%   $209.1226   $209.12   $209.10   $209.10  
  Purchase #4 $93.47   4.711%   $97.8734   $97.87   $97.85   $97.90  
  Purchase #5 $191.86   6.369%   $204.0796   $204.08   $204.10   $204.10  
  Purchase #6 $5.61   12.604%   $6.3171   $6.32   $6.30   $6.30  
  Purchase #7 $137.26   4.402%   $143.3022   $143.30   $143.30   $143.30  
  7 purchase totals = $711.52       $755.9073   $755.90   $755.85   $756.00