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 $84.89   12.469%   $95.4749   $95.47   $95.45   $95.50  
  Purchase #2 $120.53   8.467%   $130.7353   $130.74   $130.75   $130.70  
  Purchase #3 $104.90   7.245%   $112.5   $112.50   $112.50   $112.50  
  Purchase #4 $198.89   6.573%   $211.963   $211.96   $211.95   $212.00  
  Purchase #5 $40.75   6.378%   $43.349   $43.35   $43.35   $43.30  
  Purchase #6 $6.51   10.110%   $7.1682   $7.17   $7.15   $7.20  
  Purchase #7 $249.86   9.278%   $273.042   $273.04   $273.05   $273.00  
  7 purchase totals = $806.33       $874.2324   $874.23   $874.20   $874.20