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 $48.98   7.868%   $52.8337   $52.83   $52.85   $52.80  
  Purchase #2 $191.87   8.785%   $208.7258   $208.73   $208.75   $208.70  
  Purchase #3 $201.95   7.742%   $217.585   $217.59   $217.60   $217.60  
  Purchase #4 $202.36   10.535%   $223.6786   $223.68   $223.70   $223.70  
  Purchase #5 $235.87   4.432%   $246.3238   $246.32   $246.30   $246.30  
  Purchase #6 $115.77   5.292%   $121.8965   $121.90   $121.90   $121.90  
  Purchase #7 $215.54   11.834%   $241.047   $241.05   $241.05   $241.00  
  7 purchase totals = $1,212.34       $1,312.0904   $1,312.10   $1,312.15   $1,312.00