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 $249.64   7.862%   $269.2667   $269.27   $269.25   $269.30  
  Purchase #2 $87.58   4.666%   $91.6665   $91.67   $91.65   $91.70  
  Purchase #3 $134.81   5.433%   $142.1342   $142.13   $142.15   $142.10  
  Purchase #4 $25.36   10.851%   $28.1118   $28.11   $28.10   $28.10  
  Purchase #5 $165.65   11.439%   $184.5987   $184.60   $184.60   $184.60  
  Purchase #6 $192.27   12.381%   $216.0749   $216.07   $216.05   $216.10  
  Purchase #7 $118.65   8.186%   $128.3627   $128.36   $128.35   $128.40  
  7 purchase totals = $973.96       $1,060.2155   $1,060.21   $1,060.15   $1,060.30