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 $192.45   11.208%   $214.0198   $214.02   $214.00   $214.00  
  Purchase #2 $170.49   6.766%   $182.0254   $182.03   $182.05   $182.00  
  Purchase #3 $246.26   13.177%   $278.7097   $278.71   $278.70   $278.70  
  Purchase #4 $226.30   7.395%   $243.0349   $243.03   $243.05   $243.00  
  Purchase #5 $33.30   3.801%   $34.5657   $34.57   $34.55   $34.60  
  Purchase #6 $151.96   7.803%   $163.8174   $163.82   $163.80   $163.80  
  Purchase #7 $155.78   9.251%   $170.1912   $170.19   $170.20   $170.20  
  7 purchase totals = $1,176.54       $1,286.3641   $1,286.37   $1,286.35   $1,286.30