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 $96.37   12.404%   $108.3237   $108.32   $108.30   $108.30  
  Purchase #2 $8.53   9.292%   $9.3226   $9.32   $9.30   $9.30  
  Purchase #3 $185.72   5.336%   $195.63   $195.63   $195.65   $195.60  
  Purchase #4 $153.95   11.516%   $171.6789   $171.68   $171.70   $171.70  
  Purchase #5 $247.90   6.826%   $264.8217   $264.82   $264.80   $264.80  
  Purchase #6 $137.64   4.117%   $143.3066   $143.31   $143.30   $143.30  
  Purchase #7 $91.99   11.279%   $102.3656   $102.37   $102.35   $102.40  
  7 purchase totals = $922.10       $995.4491   $995.45   $995.40   $995.40