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 $55.31   8.755%   $60.1524   $60.15   $60.15   $60.20  
  Purchase #2 $132.77   5.679%   $140.31   $140.31   $140.30   $140.30  
  Purchase #3 $132.28   12.442%   $148.7383   $148.74   $148.75   $148.70  
  Purchase #4 $97.93   8.597%   $106.349   $106.35   $106.35   $106.30  
  Purchase #5 $208.96   3.764%   $216.8253   $216.83   $216.85   $216.80  
  Purchase #6 $163.47   9.712%   $179.3462   $179.35   $179.35   $179.30  
  Purchase #7 $194.72   6.807%   $207.9746   $207.97   $207.95   $208.00  
  7 purchase totals = $985.44       $1,059.6958   $1,059.70   $1,059.70   $1,059.60