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 $214.47   13.570%   $243.5736   $243.57   $243.55   $243.60  
  Purchase #2 $159.64   10.527%   $176.4453   $176.45   $176.45   $176.40  
  Purchase #3 $175.65   3.410%   $181.6397   $181.64   $181.65   $181.60  
  Purchase #4 $207.79   4.350%   $216.8289   $216.83   $216.85   $216.80  
  Purchase #5 $15.96   4.257%   $16.6394   $16.64   $16.65   $16.60  
  Purchase #6 $118.99   13.572%   $135.1393   $135.14   $135.15   $135.10  
  Purchase #7 $87.80   11.680%   $98.055   $98.06   $98.05   $98.10  
  7 purchase totals = $980.30       $1,068.3212   $1,068.33   $1,068.35   $1,068.20