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 $231.91   6.658%   $247.3506   $247.35   $247.35   $247.40  
  Purchase #2 $153.88   7.122%   $164.8393   $164.84   $164.85   $164.80  
  Purchase #3 $63.63   5.785%   $67.311   $67.31   $67.30   $67.30  
  Purchase #4 $36.81   6.259%   $39.1139   $39.11   $39.10   $39.10  
  Purchase #5 $72.75   13.672%   $82.6964   $82.70   $82.70   $82.70  
  Purchase #6 $181.99   12.738%   $205.1719   $205.17   $205.15   $205.20  
  Purchase #7 $97.56   7.184%   $104.5687   $104.57   $104.55   $104.60  
  7 purchase totals = $838.53       $911.0518   $911.05   $911.00   $911.10