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 $212.63   5.227%   $223.7442   $223.74   $223.75   $223.70  
  Purchase #2 $62.32   3.130%   $64.2706   $64.27   $64.25   $64.30  
  Purchase #3 $55.57   4.150%   $57.8762   $57.88   $57.90   $57.90  
  Purchase #4 $193.97   10.487%   $214.3116   $214.31   $214.30   $214.30  
  Purchase #5 $203.96   11.834%   $228.0966   $228.10   $228.10   $228.10  
  Purchase #6 $221.52   11.601%   $247.2185   $247.22   $247.20   $247.20  
  Purchase #7 $32.85   4.711%   $34.3976   $34.40   $34.40   $34.40  
  7 purchase totals = $982.82       $1,069.9153   $1,069.92   $1,069.90   $1,069.90