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 $56.56   6.559%   $60.2698   $60.27   $60.25   $60.30  
  Purchase #2 $122.94   8.546%   $133.4465   $133.45   $133.45   $133.40  
  Purchase #3 $195.85   3.229%   $202.174   $202.17   $202.15   $202.20  
  Purchase #4 $243.97   8.845%   $265.5491   $265.55   $265.55   $265.50  
  Purchase #5 $27.87   8.168%   $30.1464   $30.15   $30.15   $30.10  
  Purchase #6 $55.93   11.121%   $62.15   $62.15   $62.15   $62.20  
  Purchase #7 $191.64   6.492%   $204.0813   $204.08   $204.10   $204.10  
  7 purchase totals = $894.76       $957.8171   $957.82   $957.80   $957.80