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 $61.87   11.108%   $68.7425   $68.74   $68.75   $68.70  
  Purchase #2 $81.33   4.389%   $84.8996   $84.90   $84.90   $84.90  
  Purchase #3 $147.96   7.668%   $159.3056   $159.31   $159.30   $159.30  
  Purchase #4 $44.73   9.736%   $49.0849   $49.08   $49.10   $49.10  
  Purchase #5 $137.89   7.238%   $147.8705   $147.87   $147.85   $147.90  
  Purchase #6 $231.64   10.159%   $255.1723   $255.17   $255.15   $255.20  
  Purchase #7 $244.61   4.310%   $255.1527   $255.15   $255.15   $255.20  
  7 purchase totals = $950.03       $1,020.2281   $1,020.22   $1,020.20   $1,020.30