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 $181.26   13.473%   $205.6812   $205.68   $205.70   $205.70  
  Purchase #2 $235.56   10.316%   $259.8604   $259.86   $259.85   $259.90  
  Purchase #3 $14.89   13.314%   $16.8725   $16.87   $16.85   $16.90  
  Purchase #4 $110.51   13.647%   $125.5913   $125.59   $125.60   $125.60  
  Purchase #5 $62.94   11.793%   $70.3625   $70.36   $70.35   $70.40  
  Purchase #6 $21.84   13.678%   $24.8273   $24.83   $24.85   $24.80  
  Purchase #7 $24.80   11.156%   $27.5667   $27.57   $27.55   $27.60  
  7 purchase totals = $651.80       $730.7619   $730.76   $730.75   $730.90