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 $119.80   10.473%   $132.3467   $132.35   $132.35   $132.30  
  Purchase #2 $65.94   13.108%   $74.5834   $74.58   $74.60   $74.60  
  Purchase #3 $116.92   9.336%   $127.8357   $127.84   $127.85   $127.80  
  Purchase #4 $86.40   6.103%   $91.673   $91.67   $91.65   $91.70  
  Purchase #5 $167.56   9.300%   $183.1431   $183.14   $183.15   $183.10  
  Purchase #6 $158.53   11.128%   $176.1712   $176.17   $176.15   $176.20  
  Purchase #7 $243.48   5.746%   $257.4704   $257.47   $257.45   $257.50  
  7 purchase totals = $958.63       $1,043.2235   $1,043.22   $1,043.20   $1,043.20