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 $241.35   9.519%   $264.3241   $264.32   $264.30   $264.30  
  Purchase #2 $34.65   7.474%   $37.2397   $37.24   $37.25   $37.20  
  Purchase #3 $32.75   4.177%   $34.118   $34.12   $34.10   $34.10  
  Purchase #4 $111.82   9.519%   $122.4641   $122.46   $122.45   $122.50  
  Purchase #5 $230.84   5.170%   $242.7744   $242.77   $242.75   $242.80  
  Purchase #6 $245.60   8.244%   $265.8473   $265.85   $265.85   $265.80  
  Purchase #7 $93.33   13.855%   $106.2609   $106.26   $106.25   $106.30  
  7 purchase totals = $990.34       $1,073.0285   $1,073.02   $1,072.95   $1,073.00