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 $191.47   9.378%   $209.4261   $209.43   $209.45   $209.40  
  Purchase #2 $169.44   7.389%   $181.9599   $181.96   $181.95   $182.00  
  Purchase #3 $137.85   8.288%   $149.275   $149.28   $149.30   $149.30  
  Purchase #4 $69.40   5.245%   $73.04   $73.04   $73.05   $73.00  
  Purchase #5 $122.26   7.382%   $131.2852   $131.29   $131.30   $131.30  
  Purchase #6 $230.59   7.795%   $248.5645   $248.56   $248.55   $248.60  
  Purchase #7 $30.48   7.600%   $32.7965   $32.80   $32.80   $32.80  
  7 purchase totals = $951.49       $1,026.3472   $1,026.36   $1,026.40   $1,026.40