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 $216.52   11.699%   $241.8507   $241.85   $241.85   $241.90  
  Purchase #2 $23.50   12.108%   $26.3454   $26.35   $26.35   $26.30  
  Purchase #3 $132.88   7.585%   $142.9589   $142.96   $142.95   $143.00  
  Purchase #4 $53.87   13.778%   $61.2922   $61.29   $61.30   $61.30  
  Purchase #5 $229.96   8.645%   $249.84   $249.84   $249.85   $249.80  
  Purchase #6 $176.93   5.189%   $186.1109   $186.11   $186.10   $186.10  
  Purchase #7 $191.57   12.148%   $214.8419   $214.84   $214.85   $214.80  
  7 purchase totals = $1,025.23       $1,123.2400   $1,123.24   $1,123.25   $1,123.20