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 $214.40   8.452%   $232.5211   $232.52   $232.50   $232.50  
  Purchase #2 $232.48   12.148%   $260.7217   $260.72   $260.70   $260.70  
  Purchase #3 $43.54   10.378%   $48.0586   $48.06   $48.05   $48.10  
  Purchase #4 $247.83   8.386%   $268.613   $268.61   $268.60   $268.60  
  Purchase #5 $98.94   3.873%   $102.7719   $102.77   $102.75   $102.80  
  Purchase #6 $41.90   12.435%   $47.1103   $47.11   $47.10   $47.10  
  Purchase #7 $83.87   6.197%   $89.0674   $89.07   $89.05   $89.10  
  7 purchase totals = $962.96       $1,048.8640   $1,048.86   $1,048.75   $1,048.90