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 $54.96   7.818%   $59.2568   $59.26   $59.25   $59.30  
  Purchase #2 $106.49   8.592%   $115.6396   $115.64   $115.65   $115.60  
  Purchase #3 $244.74   8.110%   $264.5884   $264.59   $264.60   $264.60  
  Purchase #4 $157.29   6.591%   $167.657   $167.66   $167.65   $167.70  
  Purchase #5 $130.38   5.636%   $137.7282   $137.73   $137.75   $137.70  
  Purchase #6 $167.67   8.733%   $182.3126   $182.31   $182.30   $182.30  
  Purchase #7 $223.61   3.107%   $230.5576   $230.56   $230.55   $230.60  
  7 purchase totals = $1,085.14       $1,157.7402   $1,157.75   $1,157.75   $1,157.80