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 $87.52   9.188%   $95.5613   $95.56   $95.55   $95.60  
  Purchase #2 $243.98   11.356%   $271.6864   $271.69   $271.70   $271.70  
  Purchase #3 $147.49   13.226%   $166.997   $167.00   $167.00   $167.00  
  Purchase #4 $53.95   9.259%   $58.9452   $58.95   $58.95   $58.90  
  Purchase #5 $54.90   6.274%   $58.3444   $58.34   $58.35   $58.30  
  Purchase #6 $152.27   4.725%   $159.4648   $159.46   $159.45   $159.50  
  Purchase #7 $169.35   8.200%   $183.2367   $183.24   $183.25   $183.20  
  7 purchase totals = $909.46       $994.2358   $994.24   $994.25   $994.20