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 $33.57   8.221%   $36.3298   $36.33   $36.35   $36.30  
  Purchase #2 $137.31   8.533%   $149.0267   $149.03   $149.05   $149.00  
  Purchase #3 $216.29   7.756%   $233.0655   $233.07   $233.05   $233.10  
  Purchase #4 $89.61   4.169%   $93.3458   $93.35   $93.35   $93.30  
  Purchase #5 $57.67   9.434%   $63.1106   $63.11   $63.10   $63.10  
  Purchase #6 $219.70   7.783%   $236.7993   $236.80   $236.80   $236.80  
  Purchase #7 $159.64   4.834%   $167.357   $167.36   $167.35   $167.40  
  7 purchase totals = $913.79       $979.0347   $979.05   $979.05   $979.00