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 $114.40   9.221%   $124.9488   $124.95   $124.95   $124.90  
  Purchase #2 $21.43   8.277%   $23.2038   $23.20   $23.20   $23.20  
  Purchase #3 $39.53   13.814%   $44.9907   $44.99   $45.00   $45.00  
  Purchase #4 $142.89   11.565%   $159.4152   $159.42   $159.40   $159.40  
  Purchase #5 $64.91   4.107%   $67.5759   $67.58   $67.60   $67.60  
  Purchase #6 $168.47   10.475%   $186.1172   $186.12   $186.10   $186.10  
  Purchase #7 $84.55   13.547%   $96.004   $96.00   $96.00   $96.00  
  7 purchase totals = $636.18       $702.2556   $702.26   $702.25   $702.20