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 $112.58   3.293%   $116.2873   $116.29   $116.30   $116.30  
  Purchase #2 $28.94   13.338%   $32.8   $32.80   $32.80   $32.80  
  Purchase #3 $21.55   7.601%   $23.188   $23.19   $23.20   $23.20  
  Purchase #4 $204.56   4.549%   $213.8654   $213.87   $213.85   $213.90  
  Purchase #5 $214.82   4.205%   $223.8532   $223.85   $223.85   $223.90  
  Purchase #6 $119.47   9.418%   $130.7217   $130.72   $130.70   $130.70  
  Purchase #7 $62.70   7.337%   $67.3003   $67.30   $67.30   $67.30  
  7 purchase totals = $764.62       $808.0159   $808.02   $808.00   $808.10