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 $93.34   11.764%   $104.3205   $104.32   $104.30   $104.30  
  Purchase #2 $104.94   9.443%   $114.8495   $114.85   $114.85   $114.80  
  Purchase #3 $155.44   12.547%   $174.9431   $174.94   $174.95   $174.90  
  Purchase #4 $83.96   8.190%   $90.8363   $90.84   $90.85   $90.80  
  Purchase #5 $157.28   5.139%   $165.3626   $165.36   $165.35   $165.40  
  Purchase #6 $197.29   10.464%   $217.9344   $217.93   $217.95   $217.90  
  Purchase #7 $185.61   10.345%   $204.8114   $204.81   $204.80   $204.80  
  7 purchase totals = $977.86       $1,073.0578   $1,073.05   $1,073.05   $1,072.90