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 $240.96   5.809%   $254.9574   $254.96   $254.95   $255.00  
  Purchase #2 $184.37   6.533%   $196.4149   $196.41   $196.40   $196.40  
  Purchase #3 $67.26   6.501%   $71.6326   $71.63   $71.65   $71.60  
  Purchase #4 $93.66   11.404%   $104.341   $104.34   $104.35   $104.30  
  Purchase #5 $170.66   12.874%   $192.6308   $192.63   $192.65   $192.60  
  Purchase #6 $15.70   9.296%   $17.1595   $17.16   $17.15   $17.20  
  Purchase #7 $192.65   10.514%   $212.9052   $212.91   $212.90   $212.90  
  7 purchase totals = $965.26       $1,050.0414   $1,050.04   $1,050.05   $1,050.00