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 $234.98   8.437%   $254.8053   $254.81   $254.80   $254.80  
  Purchase #2 $239.50   7.691%   $257.9199   $257.92   $257.90   $257.90  
  Purchase #3 $68.92   4.619%   $72.1034   $72.10   $72.10   $72.10  
  Purchase #4 $48.25   8.267%   $52.2388   $52.24   $52.25   $52.20  
  Purchase #5 $181.59   11.654%   $202.7525   $202.75   $202.75   $202.80  
  Purchase #6 $46.72   5.585%   $49.3293   $49.33   $49.35   $49.30  
  Purchase #7 $144.93   8.738%   $157.594   $157.59   $157.60   $157.60  
  7 purchase totals = $964.89       $1,046.7432   $1,046.74   $1,046.75   $1,046.70