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 $37.81   10.831%   $41.9052   $41.91   $41.90   $41.90  
  Purchase #2 $168.31   6.872%   $179.8763   $179.88   $179.90   $179.90  
  Purchase #3 $209.45   6.485%   $223.0328   $223.03   $223.05   $223.00  
  Purchase #4 $66.84   10.311%   $73.7319   $73.73   $73.75   $73.70  
  Purchase #5 $76.70   5.302%   $80.7666   $80.77   $80.75   $80.80  
  Purchase #6 $156.89   8.325%   $169.9511   $169.95   $169.95   $170.00  
  Purchase #7 $21.35   10.560%   $23.6046   $23.60   $23.60   $23.60  
  7 purchase totals = $737.35       $792.8685   $792.87   $792.90   $792.90