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 $70.46   4.473%   $73.6117   $73.61   $73.60   $73.60  
  Purchase #2 $202.52   13.587%   $230.0364   $230.04   $230.05   $230.00  
  Purchase #3 $46.67   9.289%   $51.0052   $51.01   $51.00   $51.00  
  Purchase #4 $118.92   4.575%   $124.3606   $124.36   $124.35   $124.40  
  Purchase #5 $82.64   9.453%   $90.452   $90.45   $90.45   $90.50  
  Purchase #6 $5.30   12.584%   $5.967   $5.97   $5.95   $6.00  
  Purchase #7 $161.81   13.590%   $183.8   $183.80   $183.80   $183.80  
  7 purchase totals = $688.32       $759.2329   $759.24   $759.20   $759.30