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 $181.66   8.420%   $196.9558   $196.96   $196.95   $197.00  
  Purchase #2 $121.36   6.656%   $129.4377   $129.44   $129.45   $129.40  
  Purchase #3 $181.58   7.213%   $194.6774   $194.68   $194.70   $194.70  
  Purchase #4 $93.41   4.801%   $97.8946   $97.89   $97.90   $97.90  
  Purchase #5 $175.68   4.846%   $184.1935   $184.19   $184.20   $184.20  
  Purchase #6 $198.48   8.864%   $216.0733   $216.07   $216.05   $216.10  
  Purchase #7 $27.59   5.496%   $29.1063   $29.11   $29.10   $29.10  
  7 purchase totals = $979.76       $1,048.3386   $1,048.34   $1,048.35   $1,048.40