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 $204.56   13.870%   $232.9325   $232.93   $232.95   $232.90  
  Purchase #2 $133.49   5.807%   $141.2418   $141.24   $141.25   $141.20  
  Purchase #3 $200.51   4.406%   $209.3445   $209.34   $209.35   $209.30  
  Purchase #4 $226.62   6.347%   $241.0036   $241.00   $241.00   $241.00  
  Purchase #5 $92.26   6.328%   $98.0982   $98.10   $98.10   $98.10  
  Purchase #6 $185.73   10.715%   $205.631   $205.63   $205.65   $205.60  
  Purchase #7 $40.93   5.252%   $43.0796   $43.08   $43.10   $43.10  
  7 purchase totals = $1,084.10       $1,171.3312   $1,171.32   $1,171.40   $1,171.20