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 $91.91   3.624%   $95.2408   $95.24   $95.25   $95.20  
  Purchase #2 $117.45   12.436%   $132.0561   $132.06   $132.05   $132.10  
  Purchase #3 $99.26   6.839%   $106.0484   $106.05   $106.05   $106.00  
  Purchase #4 $109.39   5.505%   $115.4119   $115.41   $115.40   $115.40  
  Purchase #5 $63.74   5.211%   $67.0615   $67.06   $67.05   $67.10  
  Purchase #6 $45.84   5.288%   $48.264   $48.26   $48.25   $48.30  
  Purchase #7 $164.43   12.816%   $185.5033   $185.50   $185.50   $185.50  
  7 purchase totals = $692.02       $749.5860   $749.58   $749.55   $749.60