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 $238.91   12.643%   $269.1154   $269.12   $269.10   $269.10  
  Purchase #2 $62.78   13.310%   $71.136   $71.14   $71.15   $71.10  
  Purchase #3 $126.81   6.248%   $134.7331   $134.73   $134.75   $134.70  
  Purchase #4 $191.67   13.544%   $217.6298   $217.63   $217.65   $217.60  
  Purchase #5 $179.33   12.319%   $201.4217   $201.42   $201.40   $201.40  
  Purchase #6 $211.27   11.553%   $235.678   $235.68   $235.70   $235.70  
  Purchase #7 $88.80   7.829%   $95.7522   $95.75   $95.75   $95.80  
  7 purchase totals = $1,099.57       $1,225.4662   $1,225.47   $1,225.50   $1,225.40