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 $147.96   5.772%   $156.5003   $156.50   $156.50   $156.50  
  Purchase #2 $186.50   10.379%   $205.8568   $205.86   $205.85   $205.90  
  Purchase #3 $220.50   3.825%   $228.9341   $228.93   $228.95   $228.90  
  Purchase #4 $15.95   5.427%   $16.8156   $16.82   $16.80   $16.80  
  Purchase #5 $227.95   8.507%   $247.3417   $247.34   $247.35   $247.30  
  Purchase #6 $234.96   4.526%   $245.5943   $245.59   $245.60   $245.60  
  Purchase #7 $217.95   3.821%   $226.2779   $226.28   $226.30   $226.30  
  7 purchase totals = $1,251.77       $1,327.3207   $1,327.32   $1,327.35   $1,327.30