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 $86.48   7.116%   $92.6339   $92.63   $92.65   $92.60  
  Purchase #2 $11.72   12.324%   $13.1644   $13.16   $13.15   $13.20  
  Purchase #3 $228.55   12.351%   $256.7782   $256.78   $256.80   $256.80  
  Purchase #4 $140.73   9.150%   $153.6068   $153.61   $153.60   $153.60  
  Purchase #5 $188.55   4.758%   $197.5212   $197.52   $197.50   $197.50  
  Purchase #6 $167.73   5.106%   $176.2943   $176.29   $176.30   $176.30  
  Purchase #7 $202.32   13.106%   $228.8361   $228.84   $228.85   $228.80  
  7 purchase totals = $1,026.08       $1,118.8349   $1,118.83   $1,118.85   $1,118.80