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 $237.31   10.760%   $262.8446   $262.84   $262.85   $262.80  
  Purchase #2 $219.71   7.394%   $235.9554   $235.96   $235.95   $236.00  
  Purchase #3 $106.96   6.752%   $114.1819   $114.18   $114.20   $114.20  
  Purchase #4 $242.90   10.774%   $269.07   $269.07   $269.05   $269.10  
  Purchase #5 $117.78   12.386%   $132.3682   $132.37   $132.35   $132.40  
  Purchase #6 $183.37   11.697%   $204.8188   $204.82   $204.80   $204.80  
  Purchase #7 $93.78   5.776%   $99.1967   $99.20   $99.20   $99.20  
  7 purchase totals = $1,201.81       $1,318.4356   $1,318.44   $1,318.40   $1,318.50