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 $164.85   12.136%   $184.8562   $184.86   $184.85   $184.90  
  Purchase #2 $92.92   3.784%   $96.4361   $96.44   $96.45   $96.40  
  Purchase #3 $199.46   13.809%   $227.0034   $227.00   $227.00   $227.00  
  Purchase #4 $202.91   6.737%   $216.58   $216.58   $216.60   $216.60  
  Purchase #5 $212.80   10.216%   $234.5396   $234.54   $234.55   $234.50  
  Purchase #6 $191.94   12.370%   $215.683   $215.68   $215.70   $215.70  
  Purchase #7 $34.34   6.816%   $36.6806   $36.68   $36.70   $36.70  
  7 purchase totals = $1,099.22       $1,211.7789   $1,211.78   $1,211.85   $1,211.80