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 $154.87   6.570%   $165.045   $165.05   $165.05   $165.00  
  Purchase #2 $7.46   6.752%   $7.9637   $7.96   $7.95   $8.00  
  Purchase #3 $32.94   7.150%   $35.2952   $35.30   $35.30   $35.30  
  Purchase #4 $204.42   11.210%   $227.3355   $227.34   $227.35   $227.30  
  Purchase #5 $62.88   5.457%   $66.3114   $66.31   $66.30   $66.30  
  Purchase #6 $56.49   3.841%   $58.6598   $58.66   $58.65   $58.70  
  Purchase #7 $211.93   6.116%   $224.8916   $224.89   $224.90   $224.90  
  7 purchase totals = $730.99       $785.5022   $785.51   $785.50   $785.50