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 $24.58   3.499%   $25.4401   $25.44   $25.45   $25.40  
  Purchase #2 $26.58   11.411%   $29.613   $29.61   $29.60   $29.60  
  Purchase #3 $31.75   5.182%   $33.3953   $33.40   $33.40   $33.40  
  Purchase #4 $96.65   9.447%   $105.7805   $105.78   $105.80   $105.80  
  Purchase #5 $235.90   3.191%   $243.4276   $243.43   $243.45   $243.40  
  Purchase #6 $71.77   6.237%   $76.2463   $76.25   $76.25   $76.20  
  Purchase #7 $202.49   3.413%   $209.401   $209.40   $209.40   $209.40  
  7 purchase totals = $689.72       $723.3038   $723.31   $723.35   $723.20