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 $88.85   8.283%   $96.2094   $96.21   $96.20   $96.20  
  Purchase #2 $17.26   8.111%   $18.66   $18.66   $18.65   $18.70  
  Purchase #3 $217.48   5.712%   $229.9025   $229.90   $229.90   $229.90  
  Purchase #4 $169.75   5.673%   $179.3799   $179.38   $179.40   $179.40  
  Purchase #5 $129.91   10.374%   $143.3869   $143.39   $143.40   $143.40  
  Purchase #6 $250.34   12.223%   $280.9391   $280.94   $280.95   $280.90  
  Purchase #7 $219.87   5.789%   $232.5983   $232.60   $232.60   $232.60  
  7 purchase totals = $1,093.46       $1,181.0761   $1,181.08   $1,181.10   $1,181.10