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 $59.45   3.789%   $61.7026   $61.70   $61.70   $61.70  
  Purchase #2 $127.64   8.390%   $138.349   $138.35   $138.35   $138.30  
  Purchase #3 $194.30   4.464%   $202.9736   $202.97   $202.95   $203.00  
  Purchase #4 $241.69   7.318%   $259.3769   $259.38   $259.40   $259.40  
  Purchase #5 $238.80   5.498%   $251.9292   $251.93   $251.95   $251.90  
  Purchase #6 $91.70   7.868%   $98.915   $98.92   $98.90   $98.90  
  Purchase #7 $223.91   12.306%   $251.4644   $251.46   $251.45   $251.50  
  7 purchase totals = $1,177.49       $1,264.7107   $1,264.71   $1,264.70   $1,264.70