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 $204.80   3.150%   $211.2512   $211.25   $211.25   $211.30  
  Purchase #2 $59.65   11.553%   $66.5414   $66.54   $66.55   $66.50  
  Purchase #3 $241.54   5.157%   $253.9962   $254.00   $254.00   $254.00  
  Purchase #4 $219.54   4.872%   $230.236   $230.24   $230.25   $230.20  
  Purchase #5 $203.81   8.467%   $221.0666   $221.07   $221.05   $221.10  
  Purchase #6 $84.62   3.295%   $87.4082   $87.41   $87.40   $87.40  
  Purchase #7 $245.60   7.527%   $264.0863   $264.09   $264.10   $264.10  
  7 purchase totals = $1,259.56       $1,334.5859   $1,334.60   $1,334.60   $1,334.60