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 $80.37   9.278%   $87.8267   $87.83   $87.85   $87.80  
  Purchase #2 $183.28   3.299%   $189.3264   $189.33   $189.35   $189.30  
  Purchase #3 $123.27   5.405%   $129.9327   $129.93   $129.95   $129.90  
  Purchase #4 $130.42   9.728%   $143.1073   $143.11   $143.10   $143.10  
  Purchase #5 $139.29   12.786%   $157.0996   $157.10   $157.10   $157.10  
  Purchase #6 $142.74   11.518%   $159.1808   $159.18   $159.20   $159.20  
  Purchase #7 $72.72   8.254%   $78.7223   $78.72   $78.70   $78.70  
  7 purchase totals = $872.09       $945.1958   $945.20   $945.25   $945.10