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 $91.88   4.256%   $95.7904   $95.79   $95.80   $95.80  
  Purchase #2 $141.80   12.312%   $159.2584   $159.26   $159.25   $159.30  
  Purchase #3 $224.33   12.567%   $252.5216   $252.52   $252.50   $252.50  
  Purchase #4 $208.68   9.134%   $227.7408   $227.74   $227.75   $227.70  
  Purchase #5 $147.26   10.148%   $162.2039   $162.20   $162.20   $162.20  
  Purchase #6 $16.99   7.711%   $18.3001   $18.30   $18.30   $18.30  
  Purchase #7 $22.94   6.713%   $24.48   $24.48   $24.50   $24.50  
  7 purchase totals = $853.88       $940.2952   $940.29   $940.30   $940.30