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 $61.61   5.378%   $64.9234   $64.92   $64.90   $64.90  
  Purchase #2 $102.25   11.415%   $113.9218   $113.92   $113.90   $113.90  
  Purchase #3 $203.69   8.322%   $220.6411   $220.64   $220.65   $220.60  
  Purchase #4 $164.45   11.860%   $183.9538   $183.95   $183.95   $184.00  
  Purchase #5 $14.89   13.696%   $16.9293   $16.93   $16.95   $16.90  
  Purchase #6 $175.91   13.698%   $200.0062   $200.01   $200.00   $200.00  
  Purchase #7 $212.40   3.495%   $219.8234   $219.82   $219.80   $219.80  
  7 purchase totals = $935.20       $1,020.1990   $1,020.19   $1,020.15   $1,020.10