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 $76.88   6.723%   $82.0486   $82.05   $82.05   $82.00  
  Purchase #2 $231.75   11.213%   $257.7361   $257.74   $257.75   $257.70  
  Purchase #3 $62.30   9.311%   $68.1008   $68.10   $68.10   $68.10  
  Purchase #4 $197.83   3.183%   $204.1269   $204.13   $204.15   $204.10  
  Purchase #5 $169.47   4.638%   $177.33   $177.33   $177.35   $177.30  
  Purchase #6 $236.61   4.861%   $248.1116   $248.11   $248.10   $248.10  
  Purchase #7 $68.49   4.273%   $71.4166   $71.42   $71.40   $71.40  
  7 purchase totals = $1,043.33       $1,108.8706   $1,108.88   $1,108.90   $1,108.70