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 $162.64   6.117%   $172.5887   $172.59   $172.60   $172.60  
  Purchase #2 $87.34   12.597%   $98.3422   $98.34   $98.35   $98.30  
  Purchase #3 $105.58   12.407%   $118.6793   $118.68   $118.70   $118.70  
  Purchase #4 $32.70   7.568%   $35.1747   $35.17   $35.15   $35.20  
  Purchase #5 $245.79   10.704%   $272.0994   $272.10   $272.10   $272.10  
  Purchase #6 $86.96   12.303%   $97.6587   $97.66   $97.65   $97.70  
  Purchase #7 $217.83   6.361%   $231.6862   $231.69   $231.70   $231.70  
  7 purchase totals = $938.84       $1,026.2292   $1,026.23   $1,026.25   $1,026.30