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 $241.59   7.361%   $259.3734   $259.37   $259.35   $259.40  
  Purchase #2 $51.31   13.701%   $58.34   $58.34   $58.35   $58.30  
  Purchase #3 $36.69   13.607%   $41.6824   $41.68   $41.70   $41.70  
  Purchase #4 $43.69   4.618%   $45.7076   $45.71   $45.70   $45.70  
  Purchase #5 $177.55   11.274%   $197.567   $197.57   $197.55   $197.60  
  Purchase #6 $19.25   6.337%   $20.4699   $20.47   $20.45   $20.50  
  Purchase #7 $127.72   7.294%   $137.0359   $137.04   $137.05   $137.00  
  7 purchase totals = $697.80       $760.1762   $760.18   $760.15   $760.20