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 $93.46   3.212%   $96.4619   $96.46   $96.45   $96.50  
  Purchase #2 $156.96   9.775%   $172.3028   $172.30   $172.30   $172.30  
  Purchase #3 $11.81   11.834%   $13.2076   $13.21   $13.20   $13.20  
  Purchase #4 $246.32   10.616%   $272.4693   $272.47   $272.45   $272.50  
  Purchase #5 $92.76   7.786%   $99.9823   $99.98   $100.00   $100.00  
  Purchase #6 $181.92   9.619%   $199.4189   $199.42   $199.40   $199.40  
  Purchase #7 $225.45   12.812%   $254.3347   $254.33   $254.35   $254.30  
  7 purchase totals = $1,008.68       $1,108.1775   $1,108.17   $1,108.15   $1,108.20