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 $54.72   11.392%   $60.9537   $60.95   $60.95   $61.00  
  Purchase #2 $220.84   8.242%   $239.0416   $239.04   $239.05   $239.00  
  Purchase #3 $19.30   6.814%   $20.6151   $20.62   $20.60   $20.60  
  Purchase #4 $224.81   9.492%   $246.149   $246.15   $246.15   $246.10  
  Purchase #5 $156.51   9.234%   $170.9621   $170.96   $170.95   $171.00  
  Purchase #6 $182.35   4.779%   $191.0645   $191.06   $191.05   $191.10  
  Purchase #7 $123.74   13.783%   $140.7951   $140.80   $140.80   $140.80  
  7 purchase totals = $982.27       $1,069.5811   $1,069.58   $1,069.55   $1,069.60