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 $215.37   5.352%   $226.8966   $226.90   $226.90   $226.90  
  Purchase #2 $181.46   4.230%   $189.1358   $189.14   $189.15   $189.10  
  Purchase #3 $22.77   13.159%   $25.7663   $25.77   $25.75   $25.80  
  Purchase #4 $230.76   10.453%   $254.8813   $254.88   $254.90   $254.90  
  Purchase #5 $102.63   3.392%   $106.1112   $106.11   $106.10   $106.10  
  Purchase #6 $163.28   10.469%   $180.3738   $180.37   $180.35   $180.40  
  Purchase #7 $57.92   6.274%   $61.5539   $61.55   $61.55   $61.60  
  7 purchase totals = $974.19       $1,044.7189   $1,044.72   $1,044.70   $1,044.80