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 $204.49   12.541%   $230.1351   $230.14   $230.15   $230.10  
  Purchase #2 $151.74   9.295%   $165.8442   $165.84   $165.85   $165.80  
  Purchase #3 $110.85   3.431%   $114.6533   $114.65   $114.65   $114.70  
  Purchase #4 $57.37   9.487%   $62.8127   $62.81   $62.80   $62.80  
  Purchase #5 $216.76   12.387%   $243.6101   $243.61   $243.60   $243.60  
  Purchase #6 $193.82   4.385%   $202.319   $202.32   $202.30   $202.30  
  Purchase #7 $71.80   6.685%   $76.5998   $76.60   $76.60   $76.60  
  7 purchase totals = $1,006.83       $1,095.9742   $1,095.97   $1,095.95   $1,095.90