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 $198.69   12.642%   $223.8084   $223.81   $223.80   $223.80  
  Purchase #2 $230.90   9.852%   $253.6483   $253.65   $253.65   $253.60  
  Purchase #3 $132.41   12.117%   $148.4541   $148.45   $148.45   $148.50  
  Purchase #4 $219.30   10.789%   $242.9603   $242.96   $242.95   $243.00  
  Purchase #5 $57.51   11.845%   $64.3221   $64.32   $64.30   $64.30  
  Purchase #6 $181.70   10.384%   $200.5677   $200.57   $200.55   $200.60  
  Purchase #7 $206.57   11.332%   $229.9785   $229.98   $230.00   $230.00  
  7 purchase totals = $1,227.08       $1,363.7394   $1,363.74   $1,363.70   $1,363.80