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 $118.99   6.644%   $126.8957   $126.90   $126.90   $126.90  
  Purchase #2 $59.61   11.191%   $66.281   $66.28   $66.30   $66.30  
  Purchase #3 $181.92   12.721%   $205.062   $205.06   $205.05   $205.10  
  Purchase #4 $215.90   13.227%   $244.4571   $244.46   $244.45   $244.50  
  Purchase #5 $248.95   7.477%   $267.564   $267.56   $267.55   $267.60  
  Purchase #6 $213.85   13.659%   $243.0598   $243.06   $243.05   $243.10  
  Purchase #7 $168.29   3.475%   $174.1381   $174.14   $174.15   $174.10  
  7 purchase totals = $1,207.51       $1,327.4577   $1,327.46   $1,327.45   $1,327.60