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 $64.84   6.629%   $69.1382   $69.14   $69.15   $69.10  
  Purchase #2 $201.81   3.128%   $208.1226   $208.12   $208.10   $208.10  
  Purchase #3 $95.58   9.869%   $105.0128   $105.01   $105.00   $105.00  
  Purchase #4 $31.57   11.675%   $35.2558   $35.26   $35.25   $35.30  
  Purchase #5 $221.57   8.198%   $239.7343   $239.73   $239.75   $239.70  
  Purchase #6 $212.78   8.495%   $230.8557   $230.86   $230.85   $230.90  
  Purchase #7 $244.46   13.155%   $276.6187   $276.62   $276.60   $276.60  
  7 purchase totals = $1,072.61       $1,164.7381   $1,164.74   $1,164.70   $1,164.70