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 $93.66   12.539%   $105.404   $105.40   $105.40   $105.40  
  Purchase #2 $93.71   13.527%   $106.3862   $106.39   $106.40   $106.40  
  Purchase #3 $16.63   11.735%   $18.5815   $18.58   $18.60   $18.60  
  Purchase #4 $29.99   3.310%   $30.9827   $30.98   $31.00   $31.00  
  Purchase #5 $46.59   3.200%   $48.0809   $48.08   $48.10   $48.10  
  Purchase #6 $137.79   7.295%   $147.8418   $147.84   $147.85   $147.80  
  Purchase #7 $152.83   6.758%   $163.1583   $163.16   $163.15   $163.20  
  7 purchase totals = $571.20       $620.4354   $620.43   $620.50   $620.50