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 $219.50   6.611%   $234.0111   $234.01   $234.00   $234.00  
  Purchase #2 $68.90   7.816%   $74.2852   $74.29   $74.30   $74.30  
  Purchase #3 $32.76   13.203%   $37.0853   $37.09   $37.10   $37.10  
  Purchase #4 $100.91   5.722%   $106.6841   $106.68   $106.70   $106.70  
  Purchase #5 $14.37   3.813%   $14.9179   $14.92   $14.90   $14.90  
  Purchase #6 $31.65   11.470%   $35.2803   $35.28   $35.30   $35.30  
  Purchase #7 $228.33   10.568%   $252.4599   $252.46   $252.45   $252.50  
  7 purchase totals = $696.42       $754.7238   $754.73   $754.75   $754.80