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 $203.35   13.441%   $230.6823   $230.68   $230.70   $230.70  
  Purchase #2 $96.41   7.755%   $103.8866   $103.89   $103.90   $103.90  
  Purchase #3 $174.57   4.591%   $182.5845   $182.58   $182.60   $182.60  
  Purchase #4 $236.56   8.532%   $256.7433   $256.74   $256.75   $256.70  
  Purchase #5 $71.91   5.182%   $75.6364   $75.64   $75.65   $75.60  
  Purchase #6 $186.95   12.844%   $210.9619   $210.96   $210.95   $211.00  
  Purchase #7 $170.83   7.729%   $184.0335   $184.03   $184.05   $184.00  
  7 purchase totals = $1,140.58       $1,244.5285   $1,244.52   $1,244.60   $1,244.50