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 $127.44   11.342%   $141.8942   $141.89   $141.90   $141.90  
  Purchase #2 $192.68   4.826%   $201.9787   $201.98   $202.00   $202.00  
  Purchase #3 $171.29   10.808%   $189.803   $189.80   $189.80   $189.80  
  Purchase #4 $61.73   13.864%   $70.2882   $70.29   $70.30   $70.30  
  Purchase #5 $118.27   11.561%   $131.9432   $131.94   $131.95   $131.90  
  Purchase #6 $167.87   3.706%   $174.0913   $174.09   $174.10   $174.10  
  Purchase #7 $247.42   6.694%   $263.9823   $263.98   $264.00   $264.00  
  7 purchase totals = $1,086.70       $1,173.9809   $1,173.97   $1,174.05   $1,174.00