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 $22.59   5.784%   $23.8966   $23.90   $23.90   $23.90  
  Purchase #2 $174.76   7.436%   $187.7552   $187.76   $187.75   $187.80  
  Purchase #3 $203.30   5.198%   $213.8675   $213.87   $213.85   $213.90  
  Purchase #4 $62.35   5.754%   $65.9376   $65.94   $65.95   $65.90  
  Purchase #5 $229.80   11.497%   $256.2201   $256.22   $256.20   $256.20  
  Purchase #6 $90.94   6.192%   $96.571   $96.57   $96.55   $96.60  
  Purchase #7 $185.62   11.162%   $206.3389   $206.34   $206.35   $206.30  
  7 purchase totals = $969.36       $1,050.5869   $1,050.60   $1,050.55   $1,050.60