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 $65.86   11.136%   $73.1942   $73.19   $73.20   $73.20  
  Purchase #2 $243.65   7.726%   $262.4744   $262.47   $262.45   $262.50  
  Purchase #3 $64.74   7.665%   $69.7023   $69.70   $69.70   $69.70  
  Purchase #4 $211.57   3.608%   $219.2034   $219.20   $219.20   $219.20  
  Purchase #5 $46.27   8.530%   $50.2168   $50.22   $50.20   $50.20  
  Purchase #6 $193.79   11.572%   $216.2154   $216.22   $216.20   $216.20  
  Purchase #7 $142.43   13.592%   $161.7891   $161.79   $161.80   $161.80  
  7 purchase totals = $968.31       $1,052.7956   $1,052.79   $1,052.75   $1,052.80