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 $206.86   11.514%   $230.6779   $230.68   $230.70   $230.70  
  Purchase #2 $222.67   8.391%   $241.3542   $241.35   $241.35   $241.40  
  Purchase #3 $45.47   11.260%   $50.5899   $50.59   $50.60   $50.60  
  Purchase #4 $177.92   11.264%   $197.9609   $197.96   $197.95   $198.00  
  Purchase #5 $230.95   8.714%   $251.075   $251.08   $251.10   $251.10  
  Purchase #6 $76.96   13.838%   $87.6097   $87.61   $87.60   $87.60  
  Purchase #7 $232.84   6.741%   $248.5357   $248.54   $248.55   $248.50  
  7 purchase totals = $1,193.67       $1,307.8033   $1,307.81   $1,307.85   $1,307.90