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 $241.98   11.320%   $269.3721   $269.37   $269.35   $269.40  
  Purchase #2 $68.92   8.822%   $75.0001   $75.00   $75.00   $75.00  
  Purchase #3 $173.69   5.701%   $183.5921   $183.59   $183.60   $183.60  
  Purchase #4 $237.45   5.385%   $250.2367   $250.24   $250.25   $250.20  
  Purchase #5 $172.50   8.245%   $186.7226   $186.72   $186.70   $186.70  
  Purchase #6 $21.98   8.183%   $23.7786   $23.78   $23.80   $23.80  
  Purchase #7 $193.62   11.286%   $215.472   $215.47   $215.45   $215.50  
  7 purchase totals = $1,110.14       $1,204.1742   $1,204.17   $1,204.15   $1,204.20