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 $64.52   11.801%   $72.134   $72.13   $72.15   $72.10  
  Purchase #2 $213.58   5.224%   $224.7374   $224.74   $224.75   $224.70  
  Purchase #3 $73.52   10.454%   $81.2058   $81.21   $81.20   $81.20  
  Purchase #4 $107.52   5.555%   $113.4927   $113.49   $113.50   $113.50  
  Purchase #5 $22.59   9.538%   $24.7446   $24.74   $24.75   $24.70  
  Purchase #6 $53.77   8.434%   $58.305   $58.31   $58.30   $58.30  
  Purchase #7 $165.58   6.512%   $176.3626   $176.36   $176.35   $176.40  
  7 purchase totals = $701.08       $750.9821   $750.98   $751.00   $750.90