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 $111.34   6.670%   $118.7664   $118.77   $118.75   $118.80  
  Purchase #2 $54.80   13.729%   $62.3235   $62.32   $62.30   $62.30  
  Purchase #3 $241.93   13.372%   $274.2809   $274.28   $274.30   $274.30  
  Purchase #4 $165.74   6.125%   $175.8916   $175.89   $175.90   $175.90  
  Purchase #5 $194.34   4.513%   $203.1106   $203.11   $203.10   $203.10  
  Purchase #6 $63.71   4.659%   $66.6782   $66.68   $66.70   $66.70  
  Purchase #7 $108.73   4.722%   $113.8642   $113.86   $113.85   $113.90  
  7 purchase totals = $940.59       $1,014.9154   $1,014.91   $1,014.90   $1,015.00