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 $95.75   8.662%   $104.0439   $104.04   $104.05   $104.00  
  Purchase #2 $116.92   13.374%   $132.5569   $132.56   $132.55   $132.60  
  Purchase #3 $53.47   10.702%   $59.1924   $59.19   $59.20   $59.20  
  Purchase #4 $84.91   9.688%   $93.1361   $93.14   $93.15   $93.10  
  Purchase #5 $250.65   12.592%   $282.2118   $282.21   $282.20   $282.20  
  Purchase #6 $35.55   9.196%   $38.8192   $38.82   $38.80   $38.80  
  Purchase #7 $31.38   7.830%   $33.8371   $33.84   $33.85   $33.80  
  7 purchase totals = $668.63       $743.7974   $743.80   $743.80   $743.70