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 $159.38   6.795%   $170.2099   $170.21   $170.20   $170.20  
  Purchase #2 $218.74   4.365%   $228.288   $228.29   $228.30   $228.30  
  Purchase #3 $36.90   7.855%   $39.7985   $39.80   $39.80   $39.80  
  Purchase #4 $19.28   3.646%   $19.9829   $19.98   $20.00   $20.00  
  Purchase #5 $30.31   7.861%   $32.6927   $32.69   $32.70   $32.70  
  Purchase #6 $100.83   13.746%   $114.6901   $114.69   $114.70   $114.70  
  Purchase #7 $97.27   6.784%   $103.8688   $103.87   $103.85   $103.90  
  7 purchase totals = $662.71       $709.5309   $709.53   $709.55   $709.60